1. Field of the Invention
The present invention relates to a wireless communication system. More particularly, the present invention relates to a method and an apparatus for transmitting and receiving configuration information on Time Division Duplex (TDD) frames having a dynamic subframe.
2. Description of the Related Art
Orthogonal Frequency Division Multiplexing (OFDM) transmission is a multi-carrier transmission scheme using multiple carriers for data transmission. In OFDM, a serial input symbol stream is divided into multiple parallel streams, which are then mapped to multiple orthogonal sub-carriers. Each sub-carrier is modulated by the corresponding stream with a specified modulation scheme for transmission.
Multi-carrier modulation was first applied to high frequency military radio in the late 1950s. Although OFDM modulation techniques using multiple orthogonal sub-carriers have been developed since the 1970s, practical applications thereof have been limited owing to difficulty of implementing orthogonal modulation between multiple sub-carriers. A significant breakthrough in OFDM applicability was made in 1971 (Weinstein et al.) by applying Discrete Fourier Transform (DFT) and Inverse DFT (IDFT) to OFDM techniques. Use of DFT and IDFT has made OFDM modulation and demodulation feasible. In addition, use of guard intervals and insertion of Cyclic Prefix (CP) symbols in guard intervals have significantly reduced negative impacts of multipath reception and delay spread on the system.
Thanks to such technical advances, OFDM techniques have been applied to various digital transmission schemes, such as Digital Audio Broadcasting (DAB), Digital Video Broadcasting (DVB), Wireless Local Area Networking (WLAN) and Wireless Asynchronous Transfer Mode (WATM). That is, use of OFDM techniques had been limited owing to high hardware complexity in the past, but recent advances in various digital signal processing techniques including Fast Fourier Transform (FFT) and Inverse Fast Fourier Transform (IFFT) have made OFDM implementation practical.
Although similar to existing Frequency Division Multiplexing (FDM), OFDM is highly efficient in high speed transmission by maintaining orthogonality between multiple tones. As OFDM exhibits high frequency efficiency and is robust against multi-path fading, it can achieve optimum transmission efficiency in high speed data transmission.
Further, OFDM exhibits high frequency efficiency as it uses frequency spectra in an overlapping manner, is robust against frequency selective fading and multi-path fading, can reduce Inter-Symbol Interference (ISI) using a guard interval, can be implemented with an equalizer having a simple hardware structure, and is robust against impulse noise. With these advantages, OFDM is actively utilized for structuring communication systems.
In wireless communication, adverse channel conditions may hinder high quality data services. Channel conditions in wireless communication may frequently change owing to Additive White Gaussian Noise (AWGN), changes in received signal power due to fading, shadowing, Doppler effects due to movement and speed changes of a user equipment, and interference caused by other users and multi-path signals. Hence, effectively coping with such adverse channel conditions may be needed to support high speed and high quality data services in wireless communication.
In OFDM, modulation signals are on a two dimensional time-frequency resource grid. Resources in the time domain are distinguished by different orthogonal OFDM symbols. Resources in the frequency domain are distinguished by different orthogonal tones. That is, in the time-frequency resource grid, one OFDM symbol on the time axis and one tone on the frequency axis can specify a minimum resource unit that is referred to as a Resource Element (RE). As different resource elements are orthogonal to each other even after passing through frequency selective channels, signals sent through different resource elements can be received at the receiver side without causing interference therebetween.
A physical channel is a channel on the physical layer that is used to transmit modulation symbols obtained by modulating one or more coded bit streams. In an Orthogonal Frequency Division Multiple Access (OFDMA) system, multiple physical channels are created according to usage of information streams to be transmitted or types of receivers. The transmitter and receiver have to make a prior agreement on how to arrange a physical channel on what resource elements (mapping rule).
A wireless communication system may operate in a Frequency Division Duplex (FDD) mode or a TDD mode. In the FDD mode, two different frequencies are used for uplink and downlink transmission, and the base station and user equipment may send and receive data at the same time. In the TDD mode, the same frequency is used for uplink and downlink transmission, and the base station and user equipment cannot send and receive data at the same time. Hence, in the TDD mode, the base station and user equipment have to make a prior agreement on the time for transmission.
Therefore, a need exists for a method and an apparatus for transmitting and receiving TDD frame configuration information in a wireless communication system, wherein the base station sends TDD frame configuration information through a pre-specified region of the common control channel to thereby dynamically change the TDD frame configuration.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present invention.